The present invention relates to devices used for localized hyperthermia treatment of tumors, generally malignant tumors.
In the above technical field, it is known to treat tumors by applying a local rise in temperature. Numerous publications mention the method which consists in raising the temperature of the zone concerned to around 45xc2x0 C. so as to make the tissue sensitive to more traditional methods of treatment such as radiotherapy and chemotherapy.
Proposals have been made for some time now to treat tumors by heating the tissues to higher temperatures, around 80xc2x0 C., in order to achieve necrosis by coagulation. The objective of this development is thus no longer to prepare tissues so that they have increased sensitivity to traditional methods of treatment, but is a direct attempt at destroying tissue by localized and controlled necrosis.
To carry out such a novel method of treatment with success, proposals have been made for applicators that have a head designed to deliver heat to the tissue concerned by implementing heat-production means that rely on various physical principles. In this respect, mention can be made of microwaves, ultrasound, heating resistance elements, lasers, etc.
To undertake such treatment, the prior art comprises two kinds of proposal.
Proposals have been made for external hyperthermia applicators which are placed on the surface to treat tumors that are subcutaneous or at shallow-skin depth, or indeed directly accessible from the skin.
For tumors that are not accessible externally, proposals have also been made for xe2x80x9cintratissularxe2x80x9d applicators which are designed to be brought into the zone that is to be treated by endoscopic or endochannel means.
The present invention relates specifically to devices of the second kind, and thus concerns intratissular applicators, and more particularly applicators that use ultrasound to heat the zone(s) to be treated by means of an internal approach.
Publications which refer to such equipments describe applicators that produce an envelope of heat that is cylindrical or spherical, given the shape of the active portion of the applicator.
Thus, U.S. Pat. No. 5,620,479 describes an intratissular applicator comprising an application head that is substantially cylindrical in shape. The application head has a plurality of cylindrical ultrasound transducers connected to an electrical generator by conductor lines. The outside or emitting face of each transducer is in register with the wall of the application head which is transparent to ultrasound, while the inside face opposite from the emission face is in register with a volume of air.
Such application heads are characterized by the fact that the cylindrical transducers produce ultrasound waves that diverge, such that the quantity of heat produced, and therefore the rise in temperature, falls off very quickly with increasing distance from the heat-producing source. The effectiveness of treatment in depth in a given direction is therefore relatively limited, unless higher powers are used with the associated drawback of causing tissue in the vicinity of and/or in contact with the head to vaporize because of the increase in the amount of energy supplied by the applicator.
This gives rise to a difficulty of control in depth which is made all the more uncertain because the tissue concerned can be vascularized to a greater or lesser extent which is variable and random.
Another drawback associated with previously known applicators lies in the fact that cylindrical or spherical heads do not enable a privileged direction to be selected for treatment, and consequently do not give rise to coagulation necroses that are very well defined in a known field, i.e. that preserve the surrounding tissue which is not to be subjected to necrosis.
Another drawback of known applicators lies in the fact that the heat dispersion produced by application heads because of their omnidirectional diffusion needs to be compensated by proceeding with applications of long duration, giving rise to treatments that are relatively difficult, expensive to carry out, and highly dependent on the perfusion of the surrounding tissues.
To provide a solution to the problem of the dispersion of the emitted sound energy associated with the ultrasound waves generated by a cylindrical transducer diverging, the prior art has proposed implementing intratissular applicators having one or more transducers that generate ultrasound waves focused on one or more targets.
Thus, U.S. Pat. No. 5,402,792 describes an intratissular applicator having a head that is substantially cylindrical in shape defining a cavity in which there is placed a transducer whose emitting face is constituted by a concave acoustic lens having two acoustic focuses. The emitting face of the transducer is also covered at a distance by a leakproof membrane that is permeable to ultrasound, defining a cavity filled with degassed water to provide acoustic coupling between the emitting face and the membrane.
By using converging ultrasound waves, it is possible to concentrate the emitted acoustic-energy-in regions that are highly localized and of small extent. Nevertheless, given this small extent, it is essential to ensure that the applicator is positioned very accurately relative to the zone that is to be treated. Unfortunately, such accuracy is not always possible, depending on the region of the patient""s body that is to be treated.
In addition, the ultrasound waves emitted by a focused transducer begin by converging on a focus, after which they diverge away from the focus, such that the acoustic radiation is not uniform and the quantity of heat produced falls off very quickly on going away from the focus and away from the transducer, as is the case for a cylindrical transducer.
The present invention seeks to remedy all of the above drawbacks by proposing a novel ultrasound applicator, preferably an intratissular applicator for localized application of hyperthermia, of a design which is selected to make it possible to deliver heat in a privileged direction while ensuring good penetration for the acoustic energy and also uniform distribution thereof, and while also making omnidirectional treatment possible where necessary.
Another object of the invention is to produce an ultrasound applicator which can be used easily via an endoscopic or endochannel path, being inserted directly into a natural passage or via the operative channel of an endoscope.
To achieve the above objects, the ultrasound applicator for internally heating an ultrasound-absorbing medium presents:
an application head having at least one ultrasound transducer with an xe2x80x9cemissionxe2x80x9d face overlaid at a distance by a leakproof membrane that is transparent to ultrasound, and having another face, opposite to its emission face, that is associated with means that propagate ultrasound poorly or not at all;
means for remotely connecting the transducer to an electricity generator; and
means for providing ultrasound coupling with the membrane.
According to the invention, the applicator is characterized in that the ultrasound transducer is plane and possesses a plane emission face for emitting substantially plane ultrasound waves in a direction substantially perpendicular to the emission face.
Another object of the invention is to provide means for controlling and regulating the temperature of the application head so as to make a large temperature rise possible without running the risk of forming microbubbles of vaporization.
According to another characteristic of the invention, the applicator includes means for cooling the transducer.
The invention also provides a method of heating an ultrasound wave absorbent medium, the method being of the type consisting:
in placing an applicator having at least one ultrasound transducer (8) in or close to said medium; and
in emitting ultrasound waves from said transducer (8) in order to heat said medium.
According to the invention, the method is characterized in that it consists in implementing a plane transducer having a plane emission face for emitting ultrasound waves that are substantially plane in a direction that is substantially perpendicular to the emission face, and in heating the region of the absorbent medium that is situated in register with said emission face.
According to another characteristic of the invention, the method also consists in rotating the plane transducer so as to heat a larger volume starting from the same general position of the applicator.
According to another characteristic of the invention, the applicator then has means for rotating the transducer on its own or together with the application head.
The heating method and the applicator of the invention can be implemented specifically for localized treatment via internal passageways of regions in the human body that absorb ultrasound.
The invention thus also provides a method of therapy for applying hyperthermia treatment to a region of the human or animal body that absorbs ultrasound, the method being of the type consisting:
in placing an applicator having at least one ultrasound transducer in or in the vicinity of the region to be treated; and
in emitting ultrasound waves from the transducer to heat said region.
According to the invention, the method consists in implementing a plane transducer having a plane emission face for emitting substantially plane ultrasound waves in a direction that is substantially perpendicular to the emission face and in heating the region situated in register with the emission face.
Various other characteristics appear from the following description given with reference to the accompanying drawings which show embodiments of the invention as non-limiting examples.